I have built this recording studio a few years ago, together with Brice Sommen, fellow musician and sound engineer.
We treated all walls and ceilings acoustically, the windows can be  covered with removing panels, and the heavy entrance rolling door has been treated acoustically too. Drums are to be recorded in a separate room.
Our studio is situated in Nanterre, near Paris (France). On the photos, you can see Brice jamming with Julien Simoni, our favorite pianist.